The first known inhabitants of the modern-day United States are believed to have arrived over a period of several thousand years beginning sometime prior to 15,000 - 50,000 years ago by crossing Beringia into Alaska.[1][2] Solid evidence of these cultures settling in what would become United States territory is dated to around 14,000 years ago.[3]

The coming of Europeans began the Colonial history of the United States. The Thirteen Colonies, British colonies that would become the original U.S. states, were founded along what is now the country's east coast beginning in 1607, but various other European powers also founded settlements in what would become U.S. territory, both before and later. Due to growing disatisfaction with British rule, the thirteen British colonies fought off the British army in the American Revolutionary War of the 1770s and issued a Declaration of Independence in 1776. In early 1781, the Union of the States was legally established; half a year before the end of hostilities in the Revolutionary War. Two years later, Britain officially recognized the sovereignity and independence of the United States in the Treaty of Paris.[8] In the nineteenth century, westward expansion of United States territory began, upon the belief of Manifest Destiny, in which the United States would occupy all the North American land east to west, from the Atlantic to the Pacific Oceans. By 1912, with the admission of Arizona to the Union, the U.S. reached that goal. The outlying states of Alaska and Hawaii were both admitted in 1959.

The Progressive Era marked a time of economic growth for the United States, advancing to the Roaring Twenties. However, the Wall Street Crash of 1929 led to the Great Depression, a time of economic downturn and mass unemployment. Consequently, the U.S. government established the New Deal, a series of reform programs that intended to assist those affected by the Depression. The New Deal had varied success. However, once the U.S. entered World War II in December 1941, the economy quickly recovered, so much that the U.S. became a world superpower by the dawn of the Cold War. During the Cold War, the U.S. and the Soviet Union were the world's two superpowers, but with the end of the Cold War and the collapse of the Soviet Union, the United States became the world's only superpower.

Many indigenous peoples were semi-nomadic tribes of hunter-gatherers; others were sedentary and agricultural civilizations. Many formed new tribes or confederations in response to European colonization. Well-known groups included the Huron, Apache Tribe, Cherokee, Sioux, Delaware, Algonquin, Choctaw, Mohegan, Iroquois (which included the Mohawk nation, Oneida tribe, Seneca nation, Cayuga nation, Onondaga and later the Tuscarora tribe) and Inuit. Though not as technologically advanced as the Mesoamerican civilizations further south, there were extensive pre-Columbian sedentary societies in what is now the US. The Iroquois had a politically advanced and unique social structure that was at the very least inspirational if not directly influential to the later development of the democratic United States government, a departure from the strong monarchies from which the Europeans came.[citation needed]

A Mississippian priest, with a ceremonial flint mace. Artist Herb Roe, based on a repousse copper plate.

Mound Builder is a general term referring to the American Indians who constructed various styles of earthen mounds for burial, residential and ceremonial purposes. These included Archaic, Woodland period (Adena and Hopewell cultures), and Mississippian period Pre-Columbian cultures dating from roughly 3000 BC to the 16th century AD, and living in the Great Lakes region, the Ohio River region, and the Mississippi River region.

Mound builder cultures can be divided into roughly three eras:

Archaic era

Poverty Point in what is now Louisiana is perhaps the most prominent example of early archaic mound builder construction (c. 2500 – 1000 BC). An even earlier example, Watson Brake, dates to approximately 3400 BC and coincides with the emergence of social complexity worldwide.

Woodland period

The Archaic period was followed by the Woodland period (c. 1000 BC). Some well-understood examples would be the Adena culture of Ohio and nearby states and the subsequent Hopewell culture known from Illinois to Ohio and renowned for their geometric earthworks. The Adena and Hopewell were not, however, the only mound building peoples during this time period. There were contemporaneous mound building cultures throughout the Eastern United States.

Around 900 – 1450 AD the Mississippian culture developed and spread through the Eastern United States, primarily along the river valleys. The location where the Mississippian culture is first clearly developed is located in Illinois, and is referred to today as Cahokia.

After a period of exploration by people from various European countries, Spanish, Dutch, English, French, Swedish, and Portuguese settlements were established. Columbus first landed and encountered indigenous peoples, mainly the Arawak natives, on what is now the Bahama Islands. The natives were extremely friendly and were frequently remarked by European observers for their hospitality and belief in sharing. The Arawaks had lived in villiage communes, and had an advanced agriculture consisting of corn, yams, and cassava. They spun and wove textiles, however they had no work animals for labor. Columbus would later describe his initial encounter in his captain's log,

"They...brought us parrots and balls of cotton and spears and many other things, which they exchanged for the glass beads and hawks' bells. They willingly traded everything they owned... They were well-built, with good bodies and handsome features... They do not bear arms, and do not know them, for I showed them a sword, they took it by the edge and cut themselves out of ignorance. They have no iron. Their spears are made of cane.... They would make fine servants.... With fifty men we could subjugate them all and make them do whatever we want."

[10]Christopher Columbus was the first European to set foot on what would one day become U.S. territory when he came to Puerto Rico on November 19, 1493, during his second voyage.

In the 15th century, Europeans brought horses, cattle, and hogs to the Americas and, in turn, took back to Europe corn, potatoes, tobacco, beans, squash, and slave natives, many of which died enroute.

The strip of land along the eastern seacoast was settled primarily by English colonists in the 17th century, along with much smaller numbers of Dutch and Swedes. Colonial America was defined by a severe labor shortage that gave birth to forms of unfree labor such as slavery and indentured servitude,[16] and by a British policy of benign neglect (salutary neglect) that permitted the development of an American spirit distinct from that of its European founders.[17] Over half of all European migrants to Colonial America arrived as indentured servants.[18]

The first successful English colony was established in 1607, on the James River at Jamestown. It languished for decades until a new wave of settlers arrived in the late 17th century and established commercial agriculture based on tobacco. Between the late 1610s and the Revolution, the British shipped an estimated 50,000 convicts to its American colonies.[19] One example of conflict between Native Americans and English settlers was the 1622 Powhatan uprising in Virginia, in which Native Americans had killed hundreds of English settlers. The largest conflict between Native Americans and English settlers in the 17th century was King Philip's War in New England,[20] although the Yamasee War may have been bloodier.[21]

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The French and Indian War (1754–1763) was a watershed event in the political development of the colonies. The influence of the main rivals of the British Crown in the colonies and Canada, the French and North American Indians, was significantly reduced. Moreover, the war effort resulted in greater political integration of the colonies, as symbolized by Benjamin Franklin's call for the colonies to "Join or Die". Following Britain's acquisition of French territory in North America, King George III issued the Royal Proclamation of 1763 with the goal of organizing the new North American empire and stabilizing relations with the native Indians. In ensuing years, strains developed in the relations between the colonists and the Crown. The British Parliament passed the Stamp Act of 1765, imposing a tax on the colonies to help pay for troops stationed in North America following the British victory in the Seven Years' War. The British government felt that the colonies were the primary beneficiaries of this military presence, and should pay at least a portion of the expense. The colonists did not share this view. Rather, with the French and Indian threat diminished, the primary outside influence remained that of Britain. A conflict of economic interests increased with the right of the British Parliament to govern the colonies without representation being called into question.

The Boston Tea Party in 1773 was a direct action by colonists in the town of Boston to protest against the taxes levied by the British government. In the following two years, the relations came to a boiling point with the Intolerable Acts being passed by the British Parliament in 1774. The acts sparked outrage and resistance in the Thirteen Colonies, which formed the Continental Association passing on October 20, 1774 the Articles of Association with the aim to boycott trade with Great Britain. The First Continental Congress hoped that by imposing economic sanctions, Great Britain would be pressured to redress the grievances of the colonies, and in particular repeal the Intolerable Acts. The Congress aimed to alter Britain's policies towards the colonies without severing allegiance. Personal gain was also a notable motivation of members of the Continental Association, made up mostly of those who had economic interests that would be served by forbidding imports from Britain. In response, the British government took punitive measures aimed at making an example of Massachusetts, in order to reverse the trend of colonial resistance to parliamentary authority that had begun with the 1765 Stamp Act. Rather than give in, the Colonists boycott became operative on December 1, 1774 resulting in a sharp fall in trade with Great Britain. The British responded with the New England Restraining Act of 1775. The outbreak of the American Revolutionary War effectively superseded the American attempt to boycott British goods.

In 1781, a combined American and French Army, acting with the support of a French fleet, captured a large British army led by General Charles Cornwallis at Yorktown, Virginia. The surrender of General Cornwallis ended serious British efforts to find a military solution to their American problem.[8] In effect, "the United States was the first major colony successfully to revolt against colonial rule. In this sense, it was the first 'new nation'."[26]

Side by side with the states' efforts to gain independence through armed resistance, a political union was being developed and agreed upon by them. The first step was to formally declare independence from Great Britain. On July 4, 1776, the Second Continental Congress, still meeting in Philadelphia, declared the independence of "the United States of America" in the Declaration of Independence. Although the states were still independent entities and not yet formally bound in a legal union, July 4 is celebrated as the nation's birthday. The new nation was dedicated to principles of republicanism, which emphasized civic duty and a fear of corruption and hereditary aristocracy.[8]

A Union of the states with a constitutional government, the Congress of the Confederation first became possible with the ratification of the Articles of Confederation and Perpetual Union. The drafting of the Articles began in June 1776 and the approved text was sent to the States on November 15, 1777 for their ratification. While most States passed laws to authorize their representatives in Congress to sign the document by 1778, Maryland refused to do so until a dispute between the states concerning Western land claims had been resolved. After Virginia passed a law ceding its claims on January 2, 1781, Maryland became the 13th and final state to pass an Act to ratify the Articles on February 2, 1781. The formal signing of the Articles by Maryland was completed on March 1, 1781 in Philadelphia[27] and on the following day Samuel Huntington became the first President of the United States in Congress Assembled.[28] However, it became apparent early on that the new constitution was inadequate for the operation of the new government and efforts soon began to improve upon it.[29]

A series of attempts to organize a movement to outline and press reforms culminated in the Congress calling the Philadelphia Convention in 1787. The structure of the national government was profoundly changed on March 4, 1789, when the American people replaced the confederation type government of the Articles with a federation type government of the Constitution. The new government reflected a radical break from the normative governmental structures of the time, favoring representative, elective government with a weak executive, rather than the existing monarchical structures common within the western traditions of the time. The system of republicanism borrowed heavily from the Enlightenment ideas and classical western philosophy: a primacy was placed upon individual liberty and upon constraining the power of government through a system of separation of powers.[29] Additionally, the United States Bill of Rights was ratified on December 15, 1791 to guarantee individual liberties such as freedom of speech and religious practice and consisted of the first ten amendments of the Constitution.[30]John Jay was the first Chief Justice of the Supreme Court, whose membership was established by the Judiciary Act of 1789; the first Supreme Court session was held in New York City on February 1, 1790.[31] In 1803, the Court case Marbury v. Madison made the Court the sole arbiter of constitutionality of federal law.[32]

Native American societies reminded Europeans of a golden age only known to them in folk history.[33] The idea of freedom and democratic ideals was born in the Americas because "it was only in America" that Europeans from 1500 to 1776 knew of societies that were "truly free."[33]

“

Natural freedom is the only object of the policy of the [Native Americans]; with this freedom do nature and climate rule alone amongst them ... [Native Americans] maintain their freedom and find abundant nourishment . . . [and are] people who live without laws, without police, without religion.

As powerful, dense [Mound Builder] populations were reduced to weakened, scattered remnants, political readjustments were necessary. New confederacies were formed. One such was to become a pattern called up by Benjamin Franklin when the thirteen colonies struggled to confederate: "If the Iroquois can do it so can we", he said in substance.

Territorial expansion of the United States, omitting Oregon and other claims.

George Washington—a renowned hero of the American Revolutionary War, commander in chief of the Continental Army, and president of the Constitutional Convention—became the first President of the United States under the new U.S. Constitution. The Whiskey Rebellion in 1794, when settlers in the Pennsylvania counties west of the Allegheny Mountains protested against a federal tax on liquor and distilled drinks, was the first serious test of the federal government.[37] At the end of his second presidential term, George Washington made his farewell address, which was published in the newspaper Independent Chronicle on September 26, 1796. In his address, Washington triumphed the benefits of federal government and importance of ethics and morality while warning against foreign alliances and formation of political parties.[38] His vice president John Adams succeeded him in presidency; Adams was a member of the Federalist Party. However, the Federalists became divided after Adams sent a peace mission to France despite ongoing disputes with that nation. Thomas Jefferson, a Democratic-Republican, defeated Adams for the presidency in the 1800 election.[39]

The Louisiana Purchase, in 1803, removed the French presence from the western border of the United States and provided U.S. settlers with vast potential for expansion west of the Mississippi River.[40] Slave importation from Africa became illegal beginning in 1808, despite a growing plantation system in many southern states such as North Carolina and Georgia.[41] In response to continued British impressment of American sailors into the British Navy, the Congress declared war on Britain in 1812.[42] The United States and Britain came to a draw in the War of 1812 after bitter fighting that lasted until January 8, 1815, during the Battle of New Orleans. The Treaty of Ghent, officially ending the war, essentially resulted in the maintenance of the status quo ante bellum;[43] however, crucially for the U.S., some Native American tribes had to sign treaties with the U.S. government in response to their losses in the war.[42] During the later course of the war, the Federalists held the Hartford Convention in 1814 over concerns that the war would weaken New England. There, they proposed seven constitutional amendments meant to strengthen the region politically, but once the Federalists delivered them to Washington, D.C., the recent American victories in New Orleans and the signing of the Treaty of Ghent undermined the Federalists' arguments and contributed to the downfall of the party.[44]

The Monroe Doctrine, expressed in 1823, proclaimed the United States' opinion that European powers should no longer colonize or interfere in the Americas. This was a defining moment in the foreign policy of the United States.[15] The Monroe Doctrine was adopted in response to American and British fears over Russian and French expansion into areas of the Western Hemisphere. It was not until the Presidential Administration of Teddy Roosevelt that the Monroe Doctrine became a central tenet of American foreign policy. The Monroe Doctrine was then invoked in the Spanish-American War as well as later in the proxy wars between the United States and Soviet Union in Central America and has also essentially given developing nations in the Americas support from the United States and warned the powers in Europe to steer clear of far western affairs.[45]

In 1830, Congress passed the Indian Removal Act, which authorized the president to negotiate treaties that exchanged Indian tribal lands in the eastern states for lands west of the Mississippi River. This established Andrew Jackson, a military hero and President, as a cunning tyrant in regards to native populations. The act resulted most notably in the forced migration of several native tribes to the West, with several thousand Indians dying en route, and the Creeks' violent opposition and eventual defeat. The Indian Removal Act also directly caused the ceding of Spanish Florida and subsequently led to the many Seminole Wars.[46]

The Republic of Texas was annexed by president John Tyler in 1845.[49] The U.S., using regulars and large numbers of volunteers, defeated Mexico in 1848 during the Mexican-American War. Public sentiment in the U.S. was divided as Whigs[50] and anti-slavery forces[51] opposed the war. The 1848 Treaty of Guadalupe Hidalgo ceded California, New Mexico, and adjacent areas to the United States, which composed about thirty percent of former Mexican land. Westward expansion was enhanced further by the California Gold Rush following the discovery of gold in that state in 1848. Numerous "forty-niners" trekked to California in pursuit of gold; land-demanding European immigrants also contributed to the rising Western population.[15] In 1849 cholera spread along the California and Oregon Trail. It is believed that over 150,000 Americans died during the two cholera pandemics between 1832 and 1849.[52]

By 1860, there were nearly four million slaves residing in the United States, nearly eight times as many from 1790; within the same time period, cotton production in the U.S. boomed from less than a thousand tons to nearly one million tons per year. There were some slave rebellions - including by Gabriel Prosser (1800), Denmark Vesey (1822), and Nat Turner (1831) - but they all failed and led to tighter slave oversight in the south.[55] White abolitionist John Brown tried and failed to free a group of black slaves held in Harpers Ferry, Virginia and was therefore executed for his actions.[56]Harriet Beecher Stowe, daughter of minister Lyman Beecher, published her novel Uncle Tom's Cabin in 1852 in response to the passage of the Fugitive Slave Act. The novel intended to express her views of the cruelty of slavery and sold nearly 300,000 copies during its first year of publication and was regarded by many, including President Lincoln[citation needed], to be the book that started the Civil War.[49] Numerous slaves also escaped their masters through the Underground Railroad, a term defining secret routes where abolitionists confidentially transported runaway slaves to "free state" territory; its most famous leader was Harriet Tubman.[57]

Reconstruction took place for most of the decade following the Civil War. During this era, the "Reconstruction Amendments" were passed to expand civil rights for black Americans. Those amendments included the Thirteenth Amendment, which outlawed slavery, the Fourteenth Amendment that guaranteed citizenship for all people born or naturalized within U.S. territory, and the Fifteenth Amendment that granted the vote for all men regardless of race. While the Civil Rights Act of 1875 forbade discrimination in the service of public facilities, the Black Codes denied blacks certain privileges readily available to whites.[63] In response to Reconstruction, the Ku Klux Klan (KKK) emerged around the late 1860s as a white-supremacist organization opposed to black civil rights. Increasing hate-motivated violence from groups like the Klan influenced both the Ku Klux Klan Act of 1870 that classified the KKK as a terrorist group[64] and an 1883 Supreme Court decision nullifying the Civil Rights Act of 1875; however, in the Supreme Court case United States v. Cruikshank the Court interpreted the Fourteenth Amendment as regulating only states' decisions regarding civil rights.[65] The case defeated any protection of blacks from terrorist attacks, as did the later case United States v. Harris.[66] During the era, many regions of the southern U.S. were military-governed and often corrupt; Reconstruction ended after the disputed 1876 election between Republican candidate Rutherford B. Hayes and Democratic candidate Samuel J. Tilden. Hayes won the election, and the South soon re-entered the national political scene.[15]

Following was the Gilded Age, a term that author Mark Twain used to describe the period of the late nineteenth century when there had been a dramatic expansion of American industry. Reform of the Age included the Civil Service Act, which mandated a competitive examination for applicants for government jobs. Other important legislation included the Interstate Commerce Act, which ended railroads' discrimination against small shippers, and the Sherman Antitrust Act, which outlawed monopolies in business. Twain believed that this age was corrupted by such elements as land speculators, scandalous politics, and unethical business practices. By century's end, American industrial production and per capita income exceeded those of all other world nations and ranked only behind Great Britain. In response to heavy debts and decreasing farm prices, farmers joined the Populist Party.[67] Later, an unprecedented wave of immigration served both to provide the labor for American industry and create diverse communities in previously undeveloped areas. From 1880 to 1914, peak years of immigration, more than 22 million people migrated to the United States.[68] Abusive industrial practices led to the often violent rise of the labor movement in the United States.[69] Influential figures of the period included John D. Rockefeller and Andrew Carnegie.

After the Gilded Age came the Progressive Era, whose followers called for reform over perceived industrial corruption. Viewpoints taken by progressives included greater federal regulation of anti-trust laws and the industries of meat-packing, drugs, and railroads. Four new constitutional amendments—the Sixteenth through Nineteenth—resulted from progressive activism.[70] The era lasted from 1900 to 1918, the year marking the end of World War I.[71]

U.S. Federal government policy, since the James Monroe Administration, had been to move the indigenous population beyond the reach of the federal frontier into a series of Indian reservations. Tribes were generally forced onto small reservations as farmers and ranchers took over their lands.

Ellis Island in 1902, the main immigration port for immigrants entering the United States in the late 19th and early 20th centuries.

The United States began its rise to international power in this period with substantial population and industrial growth domestically and numerous military ventures abroad, including the Spanish-American War, which began when the United States blamed the sinking of the USS Maine on Spain. Also at stake were U.S. interests in acquiring Cuba, an island nation fighting for independence from Spanish occupation; Puerto Rico and the Philippines were also two former Spanish colonies seeking liberation. In December 1898, representatives of Spain and the U.S. signed the Treaty of Paris to end the war, with Cuba becoming an independent nation and Puerto Rico, Guam, and the Philippines becoming U.S. territories.[15][72] In 1900, Congress passed the Open Door Policy that at the time required China to grant equal trading access to all foreign nations.[15]

President Woodrow Wilson declared U.S. entry into World War I in April 1917 following a yearlong neutrality policy; the U.S. had previously shown interest in world peace by participating in the Hague Conferences. American participation in the war proved essential to the Allied victory. Wilson also implemented a set of propositions titled the Fourteen Points to ensure peace, but they were denied at the 1919 Paris Peace Conference. Isolationist sentiment following the war also blocked the U.S. from participating in the League of Nations, an important part of the Treaty of Versailles.[15]

In 1920, the manufacture, sale, import and export of alcohol was prohibited by the Eighteenth Amendment to the United States Constitution. Prohibition encouraged illegal breweries and dealers to make substantial amounts of money selling alcohol illegally. The Prohibition ended in 1933, a failure. Additionally, the KKK re-formed during that decade and gathered nearly 4.5 million members by 1924, and the U.S. government passed the Immigration Act of 1924 restricting foreign immigration.[75] The 1920s were also known as the Roaring Twenties, due to the great economic prosperity during this period. Jazz became popular among the younger generation, and thus was also called the Jazz Age.

During most of the 1920s, the United States enjoyed a period of unbalanced prosperity: farm prices and wages fell, while new industries, and industrial profits grew. The boom was fueled by an inflated stock market, which later led to the a crash on October 29, 1929.[76] The Hawley-Smoot Tariff, the Dust Bowl, and the ensuing Great Depression led to government efforts to restart the economy and help its victims with Franklin D. Roosevelt's New Deal. The recovery was rapid in all areas except unemployment, which remained fairly high until 1940.

As with World War I, the United States did not enter World War II until after the rest of the active Allied countries had done so. The United States's first contribution to the war was simultaneously to cut off the oil and raw material supplies needed by Japan to maintain its offensive in China, and to increase military and financial aid to China. Contribution came to the Allies in September 1940 in the form of the Lend-Lease program with Britain.

On December 7, 1941 Japan launched a surprise attack on the American naval base in Pearl Harbor, citing America's recent trade embargo as justification. The following day, Franklin D. Roosevelt successfully urged a joint session of Congress to declare war on Japan, calling December 7, 1941 "a date which will live in infamy". Four days after the attack on Pearl Harbor, on December 11, Nazi Germany declared war on the United States, drawing the country into a two-theater war.

Upon entering the war, the United States and its allies decided to concentrate the bulk of their efforts on fighting Hitler in Europe, while maintaining a defensive position in the Pacific until Hitler was defeated. The United States's first step was to set up a large airforce in Britain to concentrate on bombing raids into Germany itself. The American Air force relied on the B-17 Flying Fortress as its primary heavy bomber. Britain had ceased its daylight bombing raids, due to heavy casualties inflicted by the Luftwaffe. The USAAF suffered similar high losses until the introduction of the P-51 Mustang as a long range escort fighter for the bombers.

The American army's first ground action was fighting alongside the British, Australian and New Zealand armies in North Africa. By May 1943, the British 8th Army had expelled the Germans from North Africa and the Allies controlled this vital link until the end of the war. The American navy also played an active role in the Atlantic protecting the convoys bringing vital American war material to Britain. By midway through 1943, the Allies were fighting the war from Britain with unbroken supply lines, while at the same time Hitler's armies were very much on the back foot, with heavy bombing taking its toll on production.

By early 1944, a planned invasion of Western Europe was underway. What followed on June 6, 1944, was Operation Overlord, or D-Day. The largest war armada ever assembled landed on the beaches of Normandy and began the penetration of Western Europe that eventually overthrew Hitler and Nazi Germany. Following the landing at Normandy, the Americans contributed greatly to the outcome of the war, with dogged fighting in the Battle of the Ardennes and the Battle of the Bulge resulting in Allied victories against the Germans. The battles took a heavy toll on the Americans, who lost 19,000 men during the Battle of the Bulge alone. The allied bombing raids on Germany increased to unprecedented levels after the D-Day invasion, with over 70% of all bombs dropped on Germany occurring after this date. On April 30, 1945, with Berlin completely overrun with Russian forces and his country in tatters, Adolf Hitler committed suicide. On May 8, 1945, the war with Germany was over, following its unconditional surrender to the Allied forces.

Due to the United States commitment to defeating Hitler in Europe, the first years of the war against Japan was largely a defensive battle with the United States Navy attempting to prevent the Japanese Navy from asserting dominance of the Pacific region. Initially, Japan won the majority of its battles in a short period of time. Japan quickly defeated and created military bases in Guam, Thailand, Malaya, Hong Kong, Papua New Guinea, Indonesia and Burma. This was done virtually unopposed and with quicker speed than that of the German Blitzkrieg during the early stages of the war. This was important for Japan, as it had only 10% of the homeland industrial production capacity of the United States.

The turning point of the war was the Battle of Midway in June 1942. Following this, the Americans began fighting towards China where they could build an airbase suitable to commence bombing of mainland Japan with its B-29 Superfortress fleet. The Americans began by selecting smaller, lesser defended islands as targets as opposed to attacking the major Japanese strongholds. During this period, they inadvertently triggered what would become their most comprehensive victory in the entire war.

The Pacific war became the largest naval conflict in history. The American Navy emerged victorious, after at one point being stretched near to the breaking point, with almost complete destruction of the Japanese Navy. The American forces were then poised for an invasion of the Japanese mainland, to force the Japanese into unconditional surrender. On April 12th, 1945, President Franklin Delano Roosevelt died and Vice President Harry S. Truman was sworn in as the 33rd President of the United States. The use of atomic weapons against Japan was subsequently authorized. The decision to use nuclear weapons to end the conflict has been one of the most controversial decisions of the war. Supporters of the use of the bombs argue that an invasion would have cost an enormous numbers of lives, while opponents argue that the large number of civilian casualties resulting from the bombings was unjustified. The first bomb was dropped on Hiroshima on August 6th, 1945, and the second bomb was dropped on Nagasaki on August 9th, 1945. On August 15th, 1945, the Japanese surrendered unconditionally, ending World War 2.

Following World War II, the United States emerged as one of the two dominant superpowers. The U.S. Senate, on December 4, 1945, approved U.S. participation in the United Nations (UN), which marked a turn away from the traditional isolationism of the U.S. and toward more international involvement. The post-war era in the United States was defined internationally by the beginning of the Cold War, in which the United States and the Soviet Union attempted to expand their influence at the expense of the other, checked by each side's massive nuclear arsenal and the doctrine of mutual assured destruction. The result was a series of conflicts during this period including the Korean War and the tense nuclear showdown of the Cuban Missile Crisis. Within the United States, the Cold War prompted concerns about Communist influence, and also resulted in government efforts to focus mathematics and science toward efforts such as the space race.

In the decades after World War II, the United States became a global influence in economic, political, military, cultural, and technological affairs. Beginning in the 1950s, middle-class culture had a growing obsession with consumer goods.

A new consciousness of the inequality of American women began sweeping the nation, starting with the 1963 publication of Betty Friedan's best-seller, The Feminine Mystique, which explained how many housewives felt trapped and unfulfilled, assaulted American culture for its creation of the notion that women could only find fulfillment through their roles as wives, mothers, and keepers of the home, and argued that women were just as able as men to do every type of job. In 1966 Friedan and others established the National Organization for Women, or NOW, to act as an NAACP for women. Protests began, and the new "Women's Liberation Movement" grew in size and power, gained much media attention, and, by 1968, had replaced the Civil Rights Movement as the U.S.'s main social revolution. Marches, parades, rallies, boycotts, and pickets brought out thousands, sometimes millions; Friedan's Women's Strike for Equality (1970) was a nation-wide success. The Movement was factioned early on, however (NOW on the left, the Women's Equity Action League (WEAL) on the right, the National Women's Political Caucus (NWPC) in the center, and more radical groups formed by younger women on the far left). Along with Friedan, Gloria Steinem was an important feminist leader, co-founding the NWPC, the Women's Action Alliance, and editing the Movement's magazine, Ms. The proposed Equal Rights Amendment to the Constitution, passed by Congress in 1972 and favored by about seventy percent of the American public, failed to be ratified in 1982, with only three more states needed to make it law. However many federal laws (i.e. those equalizing pay, employment, education, employment opportunites, credit, ending pregnancy discrimination, and requiring NASA, the Military Academies, and other organizations to admit women), state laws (i.e. those ending spousal abuse and marital rape), Supreme Court rulings (i.e. ruling the equal protection clause of the Fourteenth Amendment applied to women), and state ERAs established women's equal status under the law, and social custom and consciousness began to change, accepting women's equality. The controversial issue of abortion, legalized in 1973 is still a point of feminist debate today.

Amid the Cold War, the United States entered the Vietnam War, whose growing unpopularity fed already existing social movements, including those among women, minorities and young people. President Lyndon B. Johnson's Great Society social programs and the judicial activism of the Warren Court added to the wide range of social reform during the 1960s and 1970s. Feminism and the environmental movement became political forces, and progress continued toward civil rights for all Americans. The Counterculture Revolution swept through the nation and much of the western world in the late sixties and early seventies, dividing the already hostile environment but also bringing forth more liberated social views.

Johnson was succeeded by President Richard Nixon in 1969, who intitially escalated the Vietnam War but soon was able to negotiate a peace treaty in 1973, effectively ending American involvement in the war. The war had cost the lives of 58,000 American troops and millions of Vietnamese. Nixon used a conflict in the Eastern Bloc between the Soviet Union and China to the advantage of the United States, bolstering relations with the People's Republic of China.[78] A new era of Cold War relations known as détente (cooperation) was begun.[79] The OPEC oil embargo led to a period of slow economic growth in 1973. Nixon's administration was brought to an ignominious close with the political scandal of Watergate in August 1974. During the years of his successor, Gerald Ford, the American-backed South Vietnamese government collapsed.

Jimmy Carter was elected in 1976 on the notion that he was not a part of the Washington political establishment.[80] The U.S. was afflicted with a recession, an energy crisis, slow economic growth, high unemployment, and high inflation coupled with high interest rates (the term stagflation was coined). On the world stage, Carter brokered the Camp David Accords between Israel and Egypt. In 1979, Iranian students stormed the U.S. embassy in Tehran and took 52 Americans hostage. Carter lost the 1980 election to Republican Ronald Reagan, whose campaign message advertised that his presidency would bring "Morning in America."[81]

Ronald Reagan produced a major realignment with his 1980 and 1984 landslides. In 1980, the Reagan coalition was possible because of Democratic losses in most social-economic groups. "Reagan Democrats" were those who usually voted Democratic, but were attracted by Reagan's policies, personality and leadership, notably his social conservatism and hawkish foreign policy. Widely regarded as a hard-line conservative[citation needed], Reagan's economic policies (dubbed "Reaganomics") and the implementation of the Economic Recovery Tax Act of 1981 lowered income taxes from 70% to 28% over the course of seven years. Reagan continued to downsize government taxation and regulation.[82] The U.S. experienced a recession in 1982; unemployment and business failures soon entered rates close to Depression-era levels. These negative trends reversed the following year, when the inflation rate decreased from 11% to 2%, the unemployment rate decreased to 7.5%, and the economic growth rate increased from 4.5 to 7.2%.[83]

Reagan took a hard line against the Soviet Union, proclaiming it to be the Evil Empire. Reagan ordered a massive buildup of the U.S. military, incurring a costly budget deficit. Reagan introduced a complicated missile defense system known as the Strategic Defense Initiative (dubbed "Star Wars" by opponents) in which the U.S. could, in theory, shoot down missiles by means of laser systems in space. Though it was never fully developed or deployed,[84] the Soviets were genuinely concerned about the possible effects of the program[85] and the research and technologies of SDI paved the way for the anti-ballistic missile systems of today.[86] The Reagan administration also provided covert funding and assistance to anti-Communist resistance movements worldwide. Reagan's interventions against Grenada and Libya were popular in the U.S., though his backing of the Contra rebels was mired in controversy.[87] The arms-for-hostages scandal led to the convictions of such figures as Oliver North and John Poindexter.[88] He shared many common views and goals with friend and ally Margaret Thatcher, the Prime Minister of the United Kingdom.[89]

Reagan met with Soviet Leader Mikhail Gorbachev, who ascended to power in 1985, four times, and their summit conferences led to the signing of the INF Treaty. Gorbachev tried to save Communism in the Soviet Union first by ending the expensive arms race with America,[90] then by shedding the East European empire in 1989. The Soviet Union collapsed in 1991, ending the US-Soviet Cold War.

The regime of Saddam Hussein in Iraq proved a continuing problem for the UN and Iraq's neighbors in its refusal to account for previously known stockpiles of chemical and biological weapons, its violations of UN resolutions, and its support for terrorism against Israel and other countries. After the 1991 Gulf War, the US, French, and British militaries began patrolling the Iraqi no-fly zones to protect Iraq's Kurdish minority and Shi’ite Arab population – both of which suffered attacks from the Hussein regime before and after the 1991 Gulf War – in Iraq's northern and southern regions, respectively.[92] In the aftermath of Operation Desert Fox during December 1998, Iraq announced that it would no longer respect the no-fly zones and resumed its efforts in shooting down Allied aircraft.[93]

During the 1990's the Al-Qaeda terrorist network and other Islamic fundamentalist groups attempted terrorist attacks against the United States and other nations. In 1993, Ramzi Yousef, a Kuwaiti national, and suspected Al-Qaeda operative, planted explosives in the underground garage of One World Trade Center and detonated them, killing six people and injuring thousands. Later that year in the Battle of Mogadishu, US Army Rangers engaged Somali militias supported by al-Qaeda in an extended firefight that cost the lives of 19 soldiers. President Clinton subsequently withdrew US combat forces from Somalia (there originally to support UN relief efforts)[94]. Terrorist attacks occurred in the 1996 Khobar Towers bombing in Saudi Arabia, and the 1998 United States embassy bombings in Tanzania and Kenya. There was an attempted bombing at Los Angeles International Airport and other attempts of acts of terrorism during the 2000 millennium attack plots. In Yemen the USS Cole was bombed in October 2000, which the government associated with Osama bin Laden's al-Qaeda terrorist network.[95]

US responses to terrorist attacks included limited cruise missile strikes on Afghanistan and Sudan (August 1998), which failed to stop al-Qaeda's leaders and their Taliban supporters. Also in 1998, President Clinton signed the Iraq Liberation Act which called for regime change in Iraq on the basis of Saddam Hussein's possession of weapons of mass destruction, oppression of Iraqi citizens and attacks upon other Middle Eastern countries.[96]

Al-Qaeda and other Islamic Fundamentalist groups were not the only groups responsible for terrorism during this time. In 1995, a domestic terrorist bombing took place at a federal building in Oklahoma City, which killed 168 people, and was the biggest terrorist attack on US soil since World War 2 at the time. It is believed that those responsible were associated with right-wing christian groups.

The presidential election in 2000 between George W. Bush (R) and Al Gore (D) was one of the closest in the U.S. history, and helped lay the seeds for political polarization to come. Although Bush won the majority of electoral votes, Gore won the majority of the popular vote. In the days following Election Day, the state of Florida entered dispute over the counting of votes due to technical issues over certain Democratic votes in some counties.[99] The Supreme Court case Bush v. Gore was decided on December 12, 2000, ending the recount with a 5-4 vote and certifying Bush as president.[100]

In response to the attacks, under the administration of President George W. Bush, the United States (with the military support of NATO and the political support of some of the international community) launched Operation Enduring Freedom which overthrew the Taliban regime which had protected and harbored bin Laden and al-Qaeda. With the support of large bipartisan majorities, the US Congress passed the Authorization for Use of Military Force Against Iraq Resolution of 2002. With a coalition of other countries including Britain, Spain, Australia, Japan and Poland, in March 2003 President Bush ordered an invasion of Iraq dubbed Operation Iraqi Freedom which led to the overthrow and capture of Saddam Hussein. Using the language of 1998 Iraq Liberation Act and the Clinton Administration, the reasons cited by the Bush administration for the invasion included the spreading of democracy, the elimination of weapons of mass destruction[101] (a key demand of the UN as well, though later investigations found parts of the intelligence reports to be inaccurate)[102] and the liberation of the Iraqi people.[103] This second invasion fueled protest marches in many parts of the world.

In August 2005, Hurricane Katrina flooded parts of the city of New Orleans and heavily damaged other areas of the gulf coast, including major damage to the Mississippi coast. The preparation and the response of the government were criticized as ineffective and slow.[104]

By 2006, rising prices saw Americans become increasingly conscious of the nation's dependence on supplies of petroleum for energy, with President Bush admitting a U.S. "addiction" to oil.[105] The possibility of serious economic disruption, should conflict overseas or declining production interrupt the flow, could not be ignored, given the instability in the Middle East and other oil-producing regions of the world. Many proposals and pilot projects for replacement energy sources, from ethanol to wind power and solar power, received more capital funding and were pursued more seriously in the 2000s than in previous decades. The 2006 midterm elections saw Congresswoman Nancy Pelosi become Speaker of the United States House of Representatives and the highest ranking woman in the history of the U.S. government.[106]

In addition to military efforts abroad, in the aftermath of 9/11 the Bush Administration increased domestic efforts to prevent future attacks. A new cabinet level agency called the United States Department of Homeland Security was created to lead and coordinate federal counterterrorism activities. The USA PATRIOT Act removed legal restrictions on information sharing between federal law enforcement and intelligence services and allowed for the investigation of suspected terrorists using means similar to those in place for other types of criminals. A new Terrorist Finance Tracking Program monitored the movements of terrorists' financial resources but was discontinued after being revealed by The New York Times.[107] Telecommunication usage by known and suspected terrorists was studied through the NSA electronic surveillance program.

Since 9/11, Islamic extremists made various attempts to attack the US homeland, with varying levels of organization and skill. For example, in 2001 vigilant passengers aboard a transatlantic flight to Miami prevented Richard Reid (shoe bomber) from detonating an explosive device.

In the presidential election of 2008, Senator Barack Obama, having narrowly defeated Senator Hillary Rodham Clinton for the Democratic nomination, ran on a platform of "Hope and Change". This, coupled with the economic crisis, helped aid his and running-mate Joe Biden's victory against the Republican ticket of Senator John McCain and Governor Sarah Palin. On November 4, Obama became the first African American to be elected President of the United States; he was sworn into office as the 44th President on January 20, 2009.